This invention concerns an ultrasonic imaging apparatus operating according to the impulse-echo technique, particularly for medical diagnosis, with an ultrasonic applicator for the linear ultrasonic scanning of a body region and an image registering device with a line generator for the formation of the echo impulses as an image line and an image generator for the displacement of successive image lines in dependence upon the displacement of the ultrasonic beam in the object, wherein the ultrasonic applicator comprises a parabolic reflector and an ultrasonic transducer head arranged for rotation about the focal line of the parabolic reflector, the head having a plurality of ultrasonic transducers which are to be focused on the reflector and which function as transmitters and/or receivers, and wherein an angle of rotation responsive signal generator is assigned to said transducers and in dependence upon the angular movement of the respective active transducer, supplies to the image generator an image line displacement voltage for displacing the successive image lines which initially has a relatively rapid rate of increase, which increases at a slower rate as the active transducer traverses a central region of the reflector, and again provides a more rapid rate of increase toward the end of a traverse of the reflector, in conformity to the variable displacement velocities of the reflected ultrasonic beam at the reflector border zones in comparison to the reflector center zone.
An ultrasonic imaging device with an ultrasonic applicator is prior art from U.S. Pat. No 3,470,868, which exhibits a cylindrical parabolic reflector, in whose focal line is disposed an ultrasonic transmitting/receiving head (with a total of two transmitting/receiving transducers) the head being arranged rotatably about the focal line as axis, and being adjustable along the focal line. During rapid rotation of the ultrasonic head about the focal line, an ultrasonic beam radiated in the direction of the reflector and reflected from the latter into a body which is to be examined, for example, is displaced parallel to itself in the body area, on account of the reflection properties of the reflector. Thus, the reflected ultrasonic beam scans this body area along a rapid succession of lines which are parallel to one another. During the corresponding linear image formation of the echo signals received from a scanning line in the body area, respectively, on a viewing screen of an oscilloscope as the display and/or recording device, a sectional view of the body region to be examined is obtained in the scanning plane. Planes parallel thereto are obtained by means of a corresponding displacement of the ultrasonic transmitting receiving head in the direction along the focal line of the parabolic reflector. However, the prior art ultrasonic imaging device has the following disadvantage. If the rotation of the rotary shaft for the ultrasonic head (employing an electric motor as the rotary drive, for example) takes place with uniform angular velocity, the beam of the respective presently active ultrasonic transmitter/receiver which is reflected by the reflector moves perpendicular to its direction of propagation in the border zones of the parabola with greater velocity (perpendicular to the direction of the parallel-proceeding sound waves) than in the central zone of the parabola. The consequence of this is that the scanning of the area under investigation does not proceed with equal velocity; thus the information density from this area is not uniform, on the one hand, and non-linear distortions occur during image registration on the other hand. Attempts have already been undertaken in order to eliminate these disadvantages at least partially. Thus, for example, in the devices according to U.S. Pat. No. 3,470,868, angle of rotation responsive signal generators have been introduced which at least provide a line displacement voltage at the image generator having the initially described variable rate of rise characteristic for the purpose of correction of non-linear distortions during image registration. However, the modulation of the image line displacement voltage took place by means of an inductive impedance change using a pair of cam plates, which in dependence upon the angular position of the respective assigned ultrasonic transducer, penetrated more or less deeply in the air gap of a high frequency generator. Angle of rotation responsive signal generators of this type are not only extremely complicated and costly from a technical point of view; in addition, accurate reproduction thereof is difficult leading to relatively high manufacturing costs. Moreover, the linearization effect is not optimal on account of the poor reproducibility of the angle responsive generator, and in addition, non-uniform information densities result. The U.S. Pat. No. 3,470,868 describes additional attempts at a solution. However, the paths of solution initiated therein are entirely of a mechanical type; that is, compensation for the non-linear effects, or the non-uniform information densities, respectively, takes place by means of engagement into the drive train of the rotary drive of the ultrasonic head in such a manner that, by means of correspondingly designed cam plates, the original drive with uniform angular velocity is converted into a drive with non-uniform velocity (such that the speed of rotation of the sound head in the region of the border zones of the reflector is slower than in the central one of the reflector). These purely mechanical solutions are also technically too complicated and likewise, as practice has shown, do not compensate for nonlinearities or variable information densities from the area under investigation to the high degree which is actually desirable.